Frequency and power factor measurement



T. AqRlcl-l 2,271,991

FREQUENCY AND POWER FACTOR MEASUREMENT Filed July 13, 1940 Feb. 3,'1942.

CYCLES P on: MINUTE Invefitor: Theodore A. Rich 1115- Attorney.

' PatentedFeb. a, 1942 FREQUENGYAND rowan micron I MEASUREMENT TheodoreA. Rich, Schenectady, N. Y., assignor to GeneralElectrlc Company,acorporation of New York Application July 13, 1940, Serial no. 345,398

Claims. (01. 112-245) lt ly invention relates to measuring apparatuswhich is highly sensitive to phase difierences in an alternating currentcircuit or circuits. It may be employed for the measurement of speed orfrequency and for the measurement of power. I

factors.

The features of my invention which arebelieved to be novel andpatentable will be pointed out in the claims appended hereto. Forabetterunderstanding of my invention, reierence is made in the followingdescription to the accompanying drawing in which Fig. 1 represents acircuit employing my invention for measuring speed; Figs. 2 and 3 showalternating voltage waves to be referred to in explaining my invention;Fig.4

shows frequency variation records taken by the instrument of myinvention; and Fig. 5 illustrates the circuit as used for themeasurement of power factor in an alternating current circuit.

In Fig. 1, represents an alternating current circuit, the frequency ofwhich it is desired to measure. Where speed is to be measured, thecircuit l0 maybe supplied by a small A. C. generator having a statorwinding II and a permanent magnet rotor l2, driven at the speed to bemeasured. In such case the voltage and frequency of circuit I0 will beproportional to the speed and a rough measurement thereof may be had bya voltmeter l3 calibrated in speed. For a more precise measurement, useis made of my invention. This consists of a'measuring instrument I4supplied from source l0 "through vacuum twin triodes' l5 and I6 placedin either i the same or separate'envelopes, which triodes are controlledby a phase shifting mutual inductance l'l supplied from the Source I0through a tuned circuit. The tuned circuit includes the primary ll ofthe mutual inductance, a variable non-inductive resistance I8 and avariable condenser IS. The mutual inductance device has an iron corecontaining an air gap. There isno appreciable load-on the secondary andthe secondary voltage is substantially in quadrature with the primarycurrent.

tubes I5 and I6 and the opposite ends of the winding 2| are connected tothe grids of the tubes through current limiting resistances 22 and I 23.If desired, the two tubes may be replaced by a single tube with twinelectrodes. 24 repre-" circuit formed by a single coil 25 having acenter top connected to one side of source It. The coil Thesecondary'winding 2| has a mid-tap connected to the filaments of theends are connected to the plates oi'the two tubes through resistances 26and 21 and a reversing switch 28. One or the resistances, i. e. 21 is Ymade adjustable. By means of the reversing switch and the variableresistance 21, the tube circuits'may be exactly balanced to compensatefor tubes which are not exactly matched. The instnmflent II has anindicating scale 29 with which the pointer cooperates and preferablyalso a recording chart 30 on which the position of the pointer isrecorded. Where the apparatus is to be used for measurement of only onesmall frequency range, such as from 59 to 60 /2 cycles, it would beunnecessary to provide for adjustment of the tuned circuit. However, animportant-feature of the apparatus is the ease by which it may beadjusted. for a wide variety of such frequency measuring ranges and forthis reason I have shown means for adjusting the value of the capacityand the noninductive resistance in the tuned circuit. For

this purpose I may use a variable capacity of the V decade variety, oras schematically represented .in Fig. l, a large number of adjustmentsteps,

each marked with the frequency at which the tuned circuit resonates forthe corresponding adjustment. For example, in Figl the condenser isadjusted to the point marked 59 and it may be assumed that the tunedcircuit is in resonance for such adjustmentwhen the frequency is 59cycles. Likewise, the condenser may be marked in speed rather than infrequency units. Thenumber of such resonant tuning steps may be verygreatly increased over the number represented and it may be assumed thatonly a small part of the capacitance adjustment range is hererepresented.

At the point ofresonan'ce, the current through theresonant circuit is inphase with the applied voltage of circuit Ill. The voltage of secondarywinding 2| is degrees out of phase with theare connected to the mid-tapof winding 2|. VI

also represents the voltage between filament and a plate of both tubessince these tubes are in effect connected across line III. cider thesecondi 55 tions, tube I5 will pass currentv when its grid and plate arepositive, 1. e. between points a and b, Fig. 2, and this current may berepresented by the shaded area I. Tube IE will pass current when itsgrid and plate are positive, i. e., be-

tween points b and c, Fig. 2, and this current may be represented by theshaded area -I. If

these currents are equal, the instrument 29 will read zero at the centerof its scale. If it does the conductor shaft connection represented at32. This is a refinement that may be used for the purpose of maintaininga constant loss in the resonance circuit for the different resonantadjustments; For example, the loss in the mutual inductance coreincreases with frequency.

' If, then, the loss in the resistance I8 is decreased not read zerounder this condition of resonance,

now, the frequency changes very slightly, the

tuned circuit is no longer in resonance, but the current therein willlead or lag the voltage V! by an amount corresponding to the change infrequency and the sharpness of tuning. The

voltage waves Vg and Vg will then shift with respect to wave VI, asrepresented, in Fig. -3. The direction of such shift will depend uponthe direction of frequency change.- Assume Fig. 3 represents an increasein frequency, the currents I and I become unbalanced in one direction.If the frequency had decreased, the unbalance would have been in theopposite direction. In

either case the instrument l4 deflects from zero and the switch '28 isthrown,'if necessary, to

cause an up-scale deflection for an increase in frequency. Thesensitivity of instrument It may easily be made such that a very smallpercentage change in frequency of circuit III will produce a fullscaledeflection of the instrument. Change in sensitivity can readily be hadby an adjustable resistance, 3! in the instrument circuit or by thenon-inductive resistance 18.

Fig. 4 showsan actual record of frequency variation taken by means ofthis invention 0n the New York Power and Light Company's 60 cyclecommercial power system at Schenectady, N. Y., showing the normalfrequency fluctuations of this well-regulated system. The record from eto f is the normal record where the width of the chart corresponds to avariation from 59.9 cycles to 60.15 cycles with a chart speed such thatthe distance from e to I along the chart represents one minute of time.At point f the sensitivity of the instrument was considerably reduced byinserting resistance at 3|, and the record from f to g shows thefrequency record Y tent as the instrument deflects from zero, means forholding the voltage constant may be inserted in the circuit as shown inFig. 5.

To the extent that the resistance in the tuned circuit changes withtemperature,'there will be a temperature error, but by proper design itcan be made small.v

It will be noted that in the circuit shown in Fig. 1, part oftheresistance I 8 is made adjust- .J 'able with the condenser adjustment byreason of I the instrument will 'be connected'to move the all) whentuning for higher frequencies by an amount sufficient to keep the totalloss constant, theinstrument scale can be calibrated in per cent changein frequency. If this-refinement is not required, the resistance I8-need not be adjustable.

In Fig. 5 I have shown my invention connected to measure the powerfactor of a single phase circuit 34. The mutual inductance and tubecircuit connections are the same as in Fig. 1. The primary I! of themutual inductance is here energized by or in proportion to the currentof line 34. The tubes are connected across the line 34 and a ballastlamp 35 is used in this circuit to hold the voltage across the tubesconstant. A

resistance 36 with a mid-tap with a sensitive D. C. instrument 3'!connected across the ends of the coil takes the place of the instrumentM in Fig. 1. The instrument 3'! will have a zero center scale marked forunity power factor, since at unity power factor the currents in bothhalves of resistance 36 will be equal and the voltage across instrument31 will be zero. When the power factor is leading, the instrument willdeflect in one direction, and when lagging, it will deflectin theopposite direction. Of course, if the power factor is always lagging,for instance, an instrument with its zero at one end of the scale may beused and this point marked for unity power factor and for lagging powerfactors pointer up scale. a

The deflection of the instrument 3'! is independent of the value ofcurrent flow in the primary H of the mutual inductance over wide rangesof currents. In Fig. 5 the normal voltage applied across the device 35and tube circuit may be of the order of 250 volts, and half of suchvoltage may be consumed in device 35. The

resistances Hand 23 may be of the order of 2 .megohms each and thevoltage across each half of secondary coil 2| may be of the order of 300volts under normal conditions. These values are not given for thepurpose of limiting the here there is very little difference because in.

Fig. 1 I actually measure the proper factor of the tuned circuit whichchanges with frequency.

' ,What I claim as new and desire to secure by Letters Patent 01' theUnited States is:

1 .Frequency measuring apparatus comprising.

a tuned circuit energized by the alternating current circuit thefrequency of which is to be measured, the power factor -of said singletuned circuit changing with the frequency and apparatus for measuringthe power factor of said tuned circuit, including an instrumentcalibrated in 'termsof frequency.

2. Frequency measuring apparatus comprising a. tuned circuit energizedby thealternating current circuit the frequency of which is to bemeascured, apparatus responsive the power factor of similar said tunedcircuit comprising twin triodes having 1 filament, grid and plateelectrodes and having their output circuits connectedto be-energ'ized inparallel by an means energized by the current of said tuned circuit forproducing an alternating volt-age in for'impressing the last mentionedvoltage between the filaments and grids of said triodes but in phaseopposition and a direct current instrument calibrated in frequency formeasuring thedifference of the current flow. through said triodes. a

3. Apparatus for measuring frequency variations' of an alternatingcurrent circuit comprisalternating voltage in phase f with thatimpressed upon said tuned circuit;

quadrature relation to such current, connections -tions of analternating current circuit comprising a circuit tuned to resonance at afrequency with? in the frequency variation range to be measured, I twintriodes having filament, grid and plate elecparallel across said tunedcircuit, a 'mutual'ine, I: 'ductance having a primary winding in serieswith 4. Apparatus for measuring'frequency variatrodes having theiroutput circuits connected in said tuned circuit and a lecondarygwindingconnected to bias'the grids .of said tr iddes in phase opposition and ameasuringinstrument calibrated ing a circuit tuned to resonance at afrequency within the frequency variation range to be measured, twintriodes having filament, grid and plate electrodes having their-outputcircuits connected in parallel across said tuned circuit, a mutual infrequency connected to measure the difference, I Y in the current flowin said triodes,'said triode circuits being adjusted to produce similarcurrent flow through both when the tuned circuitis in resonance, andmeans for varying the tuning of said tuned circuit to adapt theapparatus for inductance having 'a primary winding" in series with saidtuned circuit and a secondary winding Z connected to bias the grids ofsaid triodesin 5 phase opposition, and a measuring instrument calibratedin frequency connected to measure the difference in the current flow insaid triodes,

said triode circuits being adjusted to produce measuring frequencyvariations over diiierent frequenc'yl variationv ranges.

,5. Apparatus'as claimed in claim 4 in which the means fdrvary'ingthetuning of the tuned circuit includes variable capacity and variableresistance having their adjusting means arranged to be operated in suchrelation as to maintain the losses .in the resonant circuit constantwhen the circuit is tuned for different frequencies.

, THEQDORE A. RICH.

